1. Field of Invention
The present invention relates to an apparatus for performing a chemical vapor deposition (CVD) process in a semiconductor manufacturing process, and more particularly, for an integrated module multi-chamber CVD processing system. Furthermore, the present invention relates to a substrate processing method using the integrated module multi-chamber CVD processing system.
2. Description of Related Art
Recently, in the fabrication of semiconductors, highly integrated and finely integrated circuits of semiconductor devices have been developed. With such developments, to improve the reliability of semiconductor devices, wiring for forming semiconductor circuits plays an important role. Especially, with fine wiring for semiconductor devices, sufficient electric conductivity properties for the wiring are needed. Since fine wiring increases the current density of current flowing through it, electromigration occurs easily, causing a disconnection in the wiring. An Al film serving as the wiring material is formed by a sputtering method. In this method, step coverage is deteriorated in a fine contact hole. The film thickness on the bottom and sidewalls in the contact hole is much thinner than that on a flat surface. As a result, disconnection occurs more easily for the wiring on the bottom and sidewalls in the contact hole. Accordingly, this method causes a deterioration in the reliability of the semiconductor devices.
To form wiring around such a fine contact hole, other film deposition techniques are being widely used in place of the Al film deposition by the conventional sputtering method. One of those other techniques is a technique for forming a W film (hereafter called "blanket tungsten") using a chemical vapor deposition method (the so-called "thermal CVD method"). This method is currently getting a lot of attention. Accordingly to the chemical vapor deposition method, WF.sub.6 (6-tungsten fluoride) as a raw gas, and H.sub.2 as a reducing gas (a reducing agent) are conducted into a reaction vessel, the pressure within the reaction vessel is set to 10 to 100 Torr, and the WF.sub.6 reacts with the H.sub.2 on a substrate that is usually heated at 400.degree. to 500.degree. C. to form a W film on the substrate. Usually, this chemical reaction is necessary to be performed on the condition that the film deposition rate is dependent on the substrate temperature, that is, an elementary process on the substrate is a reaction rate-determining step.
Due to this method, a W film with a uniform film thickness can be formed even within a fine contact hole having an aperture diameter of 0.5 .mu.m and an aspect ratio (ratio of depth to width) of 2 or higher with respect to step coverage. In addition, the W film also has high resistance to electromigration with respect to the material characteristics. Therefore, it is capable of forming wiring with very high reliability, even if the wiring is fine.
An apparatus for depositing such a W film on a substrate will be described hereafter.
FIG. 9 is a schematic view showing a conventional CVD processing apparatus for forming a blanket W film using the thermal CVD method.
A substrate (3) is placed on a substrate holder (4), which is heated by lamp heaters (5) located behind the holder. The substrate, is fixed by mechanically pressing the edge of the substrate (3) by a vertically movable substrate fixture (9).
The temperature of the substrate holder (4) is measured and controlled by a thermocouple (6). The substrate (3) is placed on the substrate holder (4), which is set at a desired temperature. The substrate (3) is fixed on the substrate holder (4) by the substrate fixture (9). Reactive gas is conducted into the apparatus through the gas blow-off portion (17) located opposite the substrate (3) so as to form a desired thin film on the substrate (3) by a chemical reaction. The unreacted gas and by-product gas are expelled through an exhaust portion (2). Also, according to the technique disclosed in the specification of U.S. Pat. No. 5,033,407, purge gas (Ar gas) is conducted through a lower nozzle to prevent any film from being deposited on silica windows, and the side and back of the substrate (3).
However, the blanket W film as wiring material needs a TiW film or a TiN film as an adhesion layer on the ground. The TiW film or TiN film is formed by sputtering in a pretreatment process for the blanket W film. Here, however, no TiN or TiW film is deposited, owing to the shadow of the ring chuck used in the sputtering process, on the edge portion of the substrate. SiO.sub.2, the ground material, remains exposed on the edge portion.
If a blanket W film is deposited on the SiO.sub.2, it is apt to be peeled off in a short time after completion of the W film deposition because of the low adhesion between the blanket W film and SiO.sub.2. Unwanted peeling causes contamination due to dust particles in a reactor. Furthermore, dust particles generated in the reactor contaminate the whole substrate transfer system, resulting in a contamination of all vacuum chambers within the apparatus. Dust particles lessen productivity of the semiconductor manufacturing and lower the yield of semiconductor devices considerably.
Therefore, in the deposition process of the blanket W film, the SiO.sub.2 portion must be covered to prevent W film from being deposited on it. For this reason, for the deposition process of the blanket W film, the shape of the ring chuck must match that of the ring chuck for the sputtering process. Accordingly, the inner diameter of the ring chuck for the blanket W film deposition was designed smaller than that of the ring chuck for the sputtering process. In addition, a contact member of the ring chuck is designed to be in close contact with the entire surface of the substrate edge portion. With the close contact between the contact member of the ring chuck and substrate, reactive gas is prevented from coming into contact with the SiO.sub.2 portion, thereby preventing any W film from being deposited on the SiO.sub.2.
Here, the edge portion of the substrate is covered with a ring chuck to prevent any film from being deposited on the edge portion of the substrate with a certain width. Limiting the film deposition area in this way is called shadow formation. Also, a certain width of the edge portion of the substrate in which no film is deposited is called a shadow.
However, the conventional apparatus described above has the following problems:
When a W thin film is deposited by the chemical reaction of WF.sub.6 with H.sub.2, since the deposition rate greatly depends on the substrate temperature, the thickness uniformity of the W film to be deposited on the substrate is determined by the substrate temperature distribution. Therefore, to attain good thickness uniformity of the W film, the substrate temperature distribution must be even. Since, however, substrate fixture (9) is in contact along the edge of a substrate (3) in the above conventional apparatus, heat transfers from the substrate (3) to the substrate fixture (9) through the contact portion. Therefore, the escape of a large amount of heat from the edge portion of the substrate to the substrate fixture (9) results in a considerable drop in temperature in the vicinity of the edge of the substrate. Thus, the uniform thickness across the W film on the entire surface of the substrate is not attainable.
FIG. 13 is a view showing the sheet resistivity distribution for a W film deposited in a conventional apparatus along the radial direction of the substrate. Since the sheet resistivity is in inverse proportion to the film thickness, FIG. 13 shows that the higher the sheet resistivity of the W film is, the thinner the film thickness of the W film is. Accordingly, this means that the temperature of the substrate is lower, and therefore, the deposition rate is lower, in a place where the sheet resistivity of the W film is higher. On the contrary, the lower the sheet resistivity of the W film is, the thicker the film thickness of the W film is, and therefore, this means that the temperature is higher, and thus the deposition rate is higher in the place where the sheet resistivity is lower.
As seen in FIG. 13, the rise in the sheet resistivity in the vicinity of the edge of the substrate is noticeable, and it can be said that the temperature in the vicinity of the edge of the substrate is lower, therefore, the film thickness is thinner than that in the vicinity of the center of the substrate.
Also, the temperature distribution on the substrate (3) is sensitively responsive to that of the substrate holder (4). The temperature distribution on the substrate holder (4) is sensitively responsive to the irradiation distribution of lamp heaters (5) behind the substrate holder (4). Thus, if the irradiation distribution is nonuniform due to a nonsymmetrical lamp heater or a discontinuous lamp heater, such as a circular heater used in the conventional apparatus in FIG. 9, the temperature distribution on the substrate holder (4) becomes uneven, and thereby, the temperature distribution on the substrate (3) also becomes uneven. As a result, the thickness across the W film on the entire substrate surface becomes uneven. Also, even if uniform light irradiation from a lamp heater is applied, the temperature distribution on the surface of the substrate may not be uniform resulting from the positional relationship between the lamp heaters (5) and substrate (3), and the contact position of the substrate (3) with the substrate fixture (9). Even if uniform light irradiation from the lamp heaters could be attained, the uniform thickness across the W film on the entire substrate surface cannot be attained. Yet, in this case, it is necessary that by exposing the interiors of the reaction vessel (reactor) to the atmosphere, the positional relationship between the lamp heaters and the substrate (3), or the contact positional relationship between the substrate (3), substrate holder (4) and substrate fixture (9) is adjusted continuously.
FIG. 12 represents a contour map for the sheet resistivity distribution for a W film deposited on the substrate (3) in a conventional apparatus. Each contour line represents a constant level of sheet resistivity. To easily understand the relationship between the arrangement of the two semicircular lamp heaters and the sheet resistivity distribution, the arrangement of the semicircular lamp heaters is shown on the left side of the sheet resistivity lines. As can be easily understood from FIG. 12, the sheet resistivity is higher where the irradiation distribution from semicircular lamp heaters is not continuous in the conventional apparatus. For this reason, FIG. 12 shows that the temperature of the substrate is lower at a place where the sheet resistivity is higher.
On the other hand, the sheet resistivity is low at the bottom of the semicircular lamp heaters. Thus, it shows that the temperature of the substrate is higher where the sheet resistivity is lower. This demonstrates that the substrate temperature distribution as mentioned above greatly depends on the shape of the lamp heaters and the arrangement of lamp heaters, and therefore, the thickness across the film becomes uneven throughout the entire substrate surface.
Also, in such a conventional CVD processing apparatus as shown in FIG. 9, when a substrate (101) is fixed with a substrate fixture (102) to deposit a thin film on the substrate (101), as shown in FIG. 10, a thin film (201) is also deposited on the surface of the substrate fixture (102) which is in contact with the substrate (101). Furthermore, the thin film (201) is deposited continuously extending to the contact portion (104) of the substrate fixture (102) from the substrate (101).
For this reason, when the substrate fixture (102) is separated from the substrate (101) after the thin film depositing process has been completed, fine small pieces (202) are produced as a result of the peeling off of the thin film, as seen in FIG. 11. In other words, micro-peeling occurs and results in the production of dust particles. When the substrate fixture (102) is lifted, dust particles produced by micro-peeling drop down on the substrate (101). The dust particles caused by the micro-peeling become a major factor decreasing the production yield of semiconductor devices. The occurrence of dust particles is a serious problem as regards quality control during the manufacturing of semiconductors. FIG. 14 is an optical microphotograph showing that micro-peeling occurs on the edge portion of the region of the blanket W thin film deposited on a substrate by the conventional apparatus shown in FIG. 9.
Also, if a thin film is deposited continuously extending over the entire substrate and the contact portion between the substrate and the substrate fixture, and even if the substrate fixture comes into contact with the substrate at only one position, micro-peeling will occur, thus producing dust particles. In the CVD processing apparatus disclosed in U.S. Pat. No. 5,094,885, as easily understood from FIG. 3, which shows the contact between the substrate and clamp ring, micro-peeling occurs at several places, thus producing dust particles.
The time for deposition of a blanket tungsten film by the CVD process requires about 4 to 5 minutes. Since the deposition time in the CVD method requires about four to five times as long as that in the magnetron sputtering method, the throughput cannot be improved in a single wafer processing type CVD apparatus.
Therefore, such batch processing type CVD apparatuses as disclosed in U.S. Pat. Nos. 5,094,885 and 5,113,284 are used to deposit blanket W film. In the batch processing type CVD apparatus, however, dust particles which are produced in each of several processing stations provided within one vacuum vessel contaminate other processing stations. For this reason, the production yield for semiconductor devices cannot be improved. Furthermore, the inside of the reaction vessel is usually cleaned as one of the maintenance operations for the CVD processing apparatus. In the batch processing type CVD apparatus, when the inside of the vacuum vessel, where several processing stations are provided, is cleaned, the depositing process for a blanket W film is suspended.
Since the batch processing type reaction vessel has a larger capacity than the single wafer processing type reaction vessel, it requires more labor for cleaning, resulting in a much longer maintenance time than the latter type. Thus, in the batch processing type CVD processing apparatus, the working efficiency per week or month decreases. The resultant throughput per week or month cannot be improved. Therefore, for a blanket W film depositing process, a single wafer processing type CVD processing system is used having such a self-cleaning mechanism as disclosed in U.S. Pat. No. 5,158,644. However, in the single wafer processing type CVD processing apparatus having this self-cleaning mechanism (plasma cleaning), two processes are performed: the thin film depositing process and a cleaning process. Therefore, time for depositing thin film for a wafer requires more than twice the time for only depositing the W film. The resultant throughput cannot be improved even by this type.